build: Set default sound properites to existing files

this fixes the default values for those sounds in settings and other
troubles coming from it e.g. alarm clock

Change-Id: I824c974c2c14b6dac127dbaa1922ef2ae64721eb
Merge "build: Set default sound properites to existing files" into android-4.4
Merge pull request #15 from omnirom/android-4.4

lllkl